This application is based on applications No. 10-330379 and 10-335581 filed in Japan, the contents of which are hereby incorporated by reference.
The present invention pertains to a projecting image display device that displays images by modulating and projecting the light from a light source, and more particularly to a projecting image display device that first causes the light from the light source to form multiple light source images and then causes the light from these light source images to form an image in each pixel of the image display panel by means of a micro-lens array.
Projecting image display devices that display images by modulating and projecting light from a light source are used as projecting televisions or data projectors. Generally, the light modulation is performed by means of a liquid crystal panel. A liquid crystal panel has a number of pixels that are aligned in a two-dimensional fashion, and performs light modulation by changing the polarization of the incident light by means of its pixels so that the distribution of polarization intensity changes. The change in polarization for each pixel is individually controlled based on the image signal. The amount of light of converted polarization varies among the pixels because the degree of polarization change is different from one pixel to another. By projecting the polarized light from the pixels, which differs in amount from one pixel to another, images are displayed that have different brightnesses but which taken together comprise a meaningful image.
It is preferred that a projecting image display device display images that are bright and have uniform brightness. However, the light modulated by a liquid crystal panel comprises only the light component having a plane of polarization aligned in a certain direction, and the light component having a plane of polarization perpendicular to this light component is not used for projection. Therefore, where light is directly supplied to the liquid crystal panel from a light source that emits light having various planes of polarization, images having only half the brightness of the capacity of the light source are displayed. In addition, because the light source generally comprises a lamp, which emits light from an essentially dot-like filament, and a reflector, and the light emitted from the lamp is reflected by the reflector to perform convergence, differences in intensity easily occur between the center and the peripheral areas of the light from the light source. Where this light is led to the liquid crystal panel as is, different areas on the liquid crystal panel receive different amounts of light, resulting in uneven brightness of the displayed image.
In order to modulate and project more of the light from the light source, light comprising light rays having random planes of polarization is separated into two light components having planes of polarization perpendicular to each other, and the polarization of one of the light components is changed so that the planes of polarization of both components matches, whereupon the light is led to the liquid crystal panel. In this way, all of the light emitted from the light source is used for modulation, and the brightness of the image doubles. Normally, the separation is carried out using a polarized beam splitter (PBS) that allows one of the two light components having perpendicular planes of polarization to pass through and reflect the other; the change in polarization is performed using a half-wavelength plate that rotates the plane of polarization by 90 degrees.
Additionally, an integrator is sometimes used in order to make the intensity distribution of the light supplied to the liquid crystal panel uniform, so that the light from the light source is formed into multiple light images and the light from the light source images is led to the entire screen of the liquid crystal panel. An integrator comprises two lens arrays. By using the lens cells of the first lens array, the integrator causes the light from the light source to form images on the corresponding lens cells of the second lens array, and leads the light from the multiple light sources to the entire screen of the liquid crystal panel. In this way, the light from the center of the light ray from the light source and the light in the peripheral areas of the light ray are supplied to all areas of the liquid crystal display in a mixed fashion. As a result, the differences in light amount received by different areas of the liquid crystal panel are eliminated, whereupon an image having a uniform brightness is displayed.
A construction is also used wherein a PBS array and a half-wavelength plate are incorporated into the integrator so that harmonization of light intensity and polarization change are carried out at the same time.
In a liquid crystal panel, it is necessary to divide the pixels in order to prevent the light from adjacent pixels from becoming intermixed, and circuit components such as TFT are used in order to drive each pixel. The area where these partitions and circuit components are located is called a xe2x80x98black matrixxe2x80x99, and each pixel is surrounded by a black matrix. Light does not enter a black matrix, and if it does enter it, it does not exit, such that the light entering the black matrix cannot be used for projection. This is another obstacle to improving image brightness.
Japanese Laid-Open Patent Application Hei 9-318904 proposes the use of a micro-lens array in front of the liquid crystal panel so that the light from the integrator is caused to strike the pixel openings only, without hitting the black matrix, in order to increase the efficiency of light utilization and improve the displayed image brightness. The device of this patent application is a single-panel projecting color image display device in which pixels to modulate the red (R), green (G) and blue (B) light are alternately located on a single liquid crystal panel, and the integrator is set such that it causes the R, G and B light to form images individually. One micro-lens cell is used for each group of three pixels, i.e., R, G and B pixels.
In one embodiment, the pixels have an essentially square configuration and the micro-lens cells have an essentially hexagonal configuration. Each micro-lens cell causes the light from the integrator to form images on the corresponding group of pixels and the pixels of its surrounding groups of pixels. In another embodiment, the pixels of the liquid crystal panel have a rectangular configuration and the micro-lens cells comprise cylindrical lenses having a length three times longer than the short sides of the pixels. The cylindrical lenses are located such that their widths are parallel to the short sides of the pixels. Each micro-lens cell causes the light from the integrator to form images on the group of pixels that it faces as well as on the groups of pixels located on either side of the first pixel group.
Generally, the pixels of a liquid crystal panel used for projecting image display devices have a size of at most 30 xcexcm in order to increase image sharpness, and the F-number of the micro-lens cell that corresponds to this size is 20 or more. A micro-lens cell having such a large F-number has a poor image forming capability because of the effect of diffraction, resulting in a large blurred image. If the wavelength of light is xcex the amount of blur  less than due to diffraction is  less than =xcexxc3x97F. Therefore, using a micro-lens cell with an F-number of 20, the blur when using light having a wavelength of 400 to 700 nm (xcex=400 to 700 nm) is  less than =8 to 14 xcexcm. Therefore, where the size of the pixels is 14 xcexcm or larger, the micro-lens cell can cause almost all of the light to strike the pixels.
However, in a single-panel projection color image display device, the pixels of the liquid crystal panel flat rectangular configuration and the R, G and B pixels are often stacked together such that their short sides are aligned. The length of the short sides is often approximately one-third of that of the long sides. Therefore, even if the long sides are 30 xcexcm long, the short sides are about 10 xcexcm, and a micro-lens cell having an F-number of 20 or more cannot cause all of the light to strike the pixels.
In a projecting image display device that causes the light to strike the screen diagonally, anamorphic projection, in which the vertical magnification by means of the projection lens is different from the horizontal magnification, is used so that the vertical and horizontal lengths of the image displayed will not look unnatural. Where anamorphic projection is used, the pixels of the liquid crystal panel usually have a flat configuration to correspond to the ratio of the vertical magnification to the horizontal magnification of the projection lens. In this case as well, if the short sides of the pixels are 14 xcexcm or less, micro-lens cells having an F-number of 20 or larger cannot cause all of the light to strike the pixels.
Therefore, if micro-lens cells that cause the light to form images isotropically are used, as in the aforementioned Japanese laid-open patent application in which hexagonal micro-lens cells are used, the efficiency of light utilization in the liquid crystal panel having pixels with a flat configuration becomes low. Further, even with the micro-lens cell that causes the light to form images along the short sides of the pixels or vertically and is located such that it corresponds to one group of pixels stacked together such that their short sides are aligned, as in the cylindrical lenses of said patent application, the F-number cannot be made small and the efficiency of light utilization cannot be improved. Moreover, since this micro-lens cell does not have the capability to form images along the long sides of the pixels or horizontally, the light enters the black matrix between pixels aligned horizontally, which further reduces the light utilization efficiency of the liquid crystal panel.
In the Japanese Laid-Open Patent Applications Hei 9-318904 and Hei 10-111472, a construction is proposed in which light from multiple adjacent light sources enters micro-lens cells comprising the micro-lens array and each micro-lens cell causes the light from these light sources to form images on multiple adjacent pixels. Light from multiple light source images is supplied to one pixel by means of multiple micro-lens cells, whereby the amount of light received by each pixel becomes essentially the same.
A liquid crystal panel normally has a rectangular configuration in which its vertical and horizontal dimensions have a ratio of 3:4 or 9:16. The pixels of a liquid crystal panel are aligned in accordance with the desired quality of the displayed images, including the sharpness and the overlap of the three-color light components, which comprise color images, and therefore the ratio of the vertical pixel alignment pitch to the horizontal pixel alignment pitch does not match the ratio of the vertical side length to the horizontal side length of the liquid crystal panel.
In order to efficiently lead the light from the light source to the entire screen of the liquid crystal panel, the lens cells of the first lens array of the integrator must have essentially the same configuration as the liquid crystal panel, and the ratio of the vertical side to the horizontal side of the lens cells of the first lens array is set to be essentially identical to the ratio of the vertical side to the horizontal side of the liquid crystal panel. Therefore, the ratio of the vertical alignment pitch to the horizontal alignment pitch becomes equal to the ratio of the vertical side length to the horizontal side length of the liquid crystal panel. On the other hand, the micro-lens cells need to cause the light from the light sources formed by means of the integrator to form images on the pixels. In other words, the distribution of light source images on the liquid crystal panel must match the distribution of pixels.
However, because the ratio between the vertical alignment pitch and the horizontal alignment pitch of the first lens array lens cells is not the same as the ratio between the vertical alignment pitch and the horizontal alignment pitch of the pixels of the liquid crystal panel, if the optical axis of each lens cell of the first lens array is perpendicular to the surface of the array and the light from the light sources is made to form images on the optical axes, the distribution of the light sources thus formed does not match the distribution of the pixels. Therefore, in Japanese Laid-Open Patent Applications Hei 9-318904 and Hei 10-111472, the image forming position for the light that passes through each lens cell is made off-center by making each lens cell of the first lens array eccentric, so that the distribution of light source images will match the distribution of the pixels. The micro-lens array causes the light source images thus formed to re-form images on the liquid crystal panel without changes in distribution.
However, it is not easy to form eccentric lens cells. It takes a substantial amount of time to manufacture with sufficient precision a lens array having the desired degree of eccentricity. Consequently, if the conventional construction is used, it is difficult to improve the manufacturing efficiency for the lens array, leading to increase manufacturing costs. Moreover, it is not possible to use an optical system having a simple construction to replace the integrator as a means to form light sources that are aligned in a two-dimensional fashion.
Additionally, in the projecting image display devices in the Japanese Laid-Open Patent Applications referred to above, a transmission-type liquid crystal panel is used, and the micro-lens array is not designed to work with a reflective liquid crystal panel. In a reflective liquid crystal panel, the incident light and reflected light pass through the same light path, and therefore the micro-lens array located in front of the liquid crystal panel for the purpose of causing the light to form images on the pixels results in scattering of the reflected light. A projecting optical system having a relatively large diameter is required in order to cause the scattered reflected light to form images on the screen. Using the construction in which a conventional micro-lens array is used, it is practically impossible to display images by projecting light modulated by means of a reflective liquid crystal panel. This problem also occurs when a DMD (digital micro-mirror), which is also a reflective space modulating element, is used.
An object of the present invention is to provide an improved projecting image display device.
Another object of the present invention is to provide a projecting image display device that is capable of modulating all of the light from the light source and displaying images that are bright but which exhibits no unevenness in brightness, and that has a light modulating image display panel comprising pixels having a flat configuration.
Yet another object of the present invention is to provide a projecting image display device in which either a transmission-type or reflective image display panel may be used for the purpose of light modulation.
These objects described above are attained by means of a projecting image display device comprising a light source, a light source image forming optical system that causes the light from the light source to form multiple light source images, a liquid crystal panel that has a number of pixels aligned in a two-dimensional fashion and that modulates the light from the multiple light sources that strikes each pixel, a micro-lens array that has multiple micro-lens cells and that causes the light from the multiple light sources to form images on the pixels of the liquid crystal panel by means of each micro-lens cell, and a projecting optical system that projects the light modulated by the liquid crystal panel onto the screen, wherein each pixel of the liquid crystal panel has a flat configuration which is long in a first direction and short in a second direction perpendicular to the first direction, and wherein each micro-lens cell of the micro-lens array has a flat configuration which is long in the second direction and short in the first direction.
The objects described above are also attained by means of a projecting image display device comprising a light source, a light source image forming optical system that causes the light from the light source to form multiple light source images aligned in a two-dimensional fashion, a liquid crystal panel that has a number of pixels aligned in a two-dimensional fashion and that modulates the light from the multiple light source images that strikes each pixel, an image forming optical system that causes the light from the multiple light source images to form images on the pixels of the liquid crystal panel, and a projecting optical system that projects the light modulated by the liquid crystal panel onto the screen, wherein the light source image forming optical system forms multiple light source images such that the distribution of the light source images matches the distribution obtained by multiplying the distribution of the pixels of the liquid crystal panel using different magnifications for the two sides perpendicular to each other and wherein the image forming optical system comprises two cylindrical lens arrays that have different focal lengths and that form images on planes that are perpendicular to each other, said image forming optical system causing the light from the multiple light source images to form images such that the resulting images have a distribution matching the distribution of the pixels of the liquid crystal.